Milo g



(No Model.)

M. G. KELLOGG. MULTIPLE SWITGHBOARD.

Patented Odt. 26,1897.

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I a n UNITED STATES PATENT ()FFICE.

MILO G. KELLOGG, OF CHICAGO, ILLINOIS, ASSIGNOR TO THE KELLOGG SIVITCHBOARD AND SUPPLY COMPANY, OF SAME PLACE.

M ULTIPLE SWITCHBOARD.

SPECIFICATION forming part of Letters Patent No. 592,321, dated October 26, 1897.

- Application filed November 29, 1889 $erial No. 332,024. (No model.)

Tc all whom it may concern: 1

Be it known that I, MILO G. KELLOGG, of Chicago,lllinois,temporarily residing at S tuttgart,in the Empire of Germany,have invented certain new and useful Improvements in Multiple Switchboards for Telephone-Exchanges, of which the following isa full, clear, concise, and exact description, reference being had to the accompanying drawings, forming a part of this specification.

My invention relates to a single-circuit telephone system; and it consists in a system of testing such lines to determine whether they are in use.

In the accompanying drawings, illustrating my invention, Figures 1 and 1 are front views of sections of two multiple switchboards to which the same lines are connected. Fig. 2 is a diagram illustrating the main-line switchboards, apparatus, and connections necessary to illustrate my invention. Fig. 3 shows a diagram of an operators cord system to be used in connection with said boards. Fig. 4 is a diagram of a subscribers-station apparatus necessary to illustrate my invention. Fig. 5 shows an operators test system to be used at the boards.

G in each case of the drawings represents a ground connection. I

Like parts and apparatus are designated by the same letters and figures of reference.-

In Fig. 2, A is a sectional view of the switchboard shown in Fig. 1, and A is a sectional View of the switchboard shown in Fig. 1", each as indicated by the line (1 c.

There are as many boards in the exchange as are necessary for the number of lines. On each board is a spring-jack or similar switch for each line. Each switch has a contactspring which normally bears on an insulated contact-point and has a contact-piece insulated from the rest (except by the circuit con nections) and is adapted to receive a switchplug and when a plug is inserted to disconnect the spring from the contact-point and form connection between the spring and the contact-piece of the plug.

In Fig. 2, g 9 represent the springs of the diiferent switches, h h the contact-points on which the springs normally bear, and j j the insulated contact-pieces.

a plug is inserted into a switch it operates it,

as above described. The contact-pieces jj should be so placed that a test-plug may be readily applied to them. Their only function is to form test-pieces for their lines, and they may be placed as shown or in any convenient position on their boards.

The connections of a line to the switchboards is as follows and as shown: A line normally grounded at the central office passes successively through the pairs of contactpoints of its switches on the several boards, passing in each case to the spring first. It then passes through an annunciator and resistance-coil to ground.

to is the annunciator, and 0c is the resistancecoil. connected to the line, the connection being between the switch-p0ints and the resistance of the annunciator and resistance-coil. In lines which are normally open to the ground at the central office the line, after passing through the pairs of contact-points of its switches, is connected to its contact-pieces jj. Independent calling-circuits are generally used for such lines, such as the Law and American district systems. Line No. 1, as indicated, shows the connection of aline normally grounded and line No. 2 the connection of a line normally open at the central office.

Fig. 3 shows an operators cord system with one pair of cords and their plugs, switch, annnnciator, and the operators telephone and calling generator or battery. The plugs DD are constructed substantially as shown, m' m being the rubber insulations and n n the contact-pieces, and they should be inserted into the switches in such a position that the contact-pieceof the plug forms connection with the contact-spring of the switch and is not in connection with the contact-piece j.

0 is a metal plate on which the bases of the plugs normally rest and which then connects the contact-pieces of the plugs with the ground.

The contact-pieces jj of the line are Y is the looping-in switch, and v is the clearing-out annunciator of the pair of cords.

t is the operators telephone, and B is her calling generator or battery.

The looping-in switch Y has two levers'and three pairs of contact-bolts, on each pair of which the levers may be alternately placed.

The levers are connected together by an insulated cross-piece with a knob by which the operator may at will move the levers by one motion from the pair of contact-bolts on which they normally rest to the next adjoining pair' of bolts, and thence to the remaining pair of bolts.- The pair of contact-bolts on which the levers normally rest are connected together through the operators telephone. The next adjoining pair are connected together through the generator, and the remaining pair are connected together through the clearing-out annunciator. The contact-pieces of the two switch-plugs, are connected by means out of circuit, and finally the two lines are connected together through the annunciator. By one motion, therefore, the operator first rings the bell of the subscriber wanted and then leaves the lines connected together for conversation with a clearing-out annunciator in the circuit.

The method of connecting other pairs of cords with their accompanying apparatus to the system as Well as the method of operating the system in connection with the switchboards will be apparent to those skilled in the art. Each operator has one cord system with as many pairs of cords as she may need, and the parts are conveniently mounted and arranged for her work.

In the subscribers-station apparatus shown in. Fig. 4:, l is the magneto-bell containing a calling-generator, 2 is the telephone, 3 is the telephone-switch, and 4 is a condenser of suitable capacity. The contact-points and circuits are as shown or otherwise arranged so as to substantially perform the operations hereinafter described. The condenser is in the circuit with the line and telephone when the telephone is taken from the switch for use,

I and it is switched from the circuit of the line when the telephone is placed on the switch.

In the operato'rs test system shown in Fig.

5, T is the test-plug, S is the test receiving instrument, B is the test-battery, and G is the ground connection. The several parts are connected as shown. The test receiving instrument and the battery should be so adjusted to each other and to the circuits that the instrument will respond or sound when the plug is placed on a test contact-piece jof a line and the subscribers telephone is on its switch and the circuitto the line is not opened by the line being switched at one of the boards, but will not sound when the line is switched or when the telephone at the subscribers station is oif from its switch, so that the condenser is in the circuit. ance of the ofiice ground connection of the line through the annunciator and resistancecoil should be made large enough so as not to permit enough current to pass through the test instrument to operate the instrument or the annunciator when the testis made. The amount of this resistance will depend on the form and construction of the other parts. The annunciator-magnet might in cases be constructed with sufticient resistance so that no other coil would be required. The system of testing is as follows: An operator, on testing, places the contact-piece T of her test system on the test contact-piece j of the line tested at her board. If the line is not switched at any board, a complete circuit is established from the ground through thetest receiving instrument and battery to the line, and if the subscribers telephone is on the switch to the ground through his signal-bell circuit the instrument will sound, indicating that the line is free. If, however, the line is switched at any board or if the telephone is oif from its switch and the condenser is in the circuit, the circuit will be open, so that the test receiving instrument will not sound. The operator will therefore know when the instrument does sound. that either the line is switched or the subscriber has removed his telephone from the switch for use and she will not switch the line with another one. Each operator has a test-plug and test receiving instrument connected substantially as shown.

The condenser properly constructed and connected in the circuit as shown will not materially aifect the continuity of the circuit for the telephone-current.

The use of the resistance-coils in the groundcircuit of the lines, even were they made of several hundred ohms resistance each, would not materially affect the working of the system, as magneto-generators now in use are constructed to operate the signal-bells and annunciators through circuits of several thousand ohms resistance.

The test system depends on the fact that an electromagnet, with an armature and a retractile spring acting on the armature, may readily be made to move or attract the armature when in closed circuit with a battery and a certain resistance and notto attract .the armature when in closed circuit withthe battery and a considerably-greater resistance,

whereby the amount of current passing .The resistcreased. This construction and adjustment would depend on the style of the electromagnet, the strength of the retractile spring, and the resistances of the circuit and could easily be obtained. W'hen the test is made as above. described and neither the line is switched for use nor the subscribers telephone is switched for use, the test-circuit is from the ofiice ground through the test-battery and test receiving instrument to the contact to which the plug is supplied, and thence to ground in two derived circuits, one through the resistance-coil of relatively high resistance at the central office and the other through the circuit of the normally closed pairs of contacts of the line to the ground at the subscribers station. The test receiving instruments are so adjusted to the circuits and the battery that when the line is neither switched nor the subscribers telephone is switched for use the instrument will sound or respond. It is, however, so adjusted that either when the line is switched for conversation and the derived circuit to ground at the subscribers station is thereby opened or the subscribers telephone is switched for use and the condenser is thereby includedin the line-circuit, (in either case opening to battery-currents the derived circuit in which they are included,) and therefore increasing the resistance of the closed circuit in which the test instrument and battery are included, there will not be sufficient current passing through the instrument to cause it to be operated, al-' though there will be some current passing through it which will tend to cause it to operate.

In multiple-switchboard systems an operator to whom certain lines are assigned to answer frequently receives several calls at practically the same moment, and it may re-- quire some time before she can switch to a certain line and answer its call. In systems in which the test depends only on the switching of the line at some other board another operator may in the meantime test the line, and, finding it to test free, may switch it to another line and cause annoyance and confusion to the subscriber. In this system this trouble is obviated, because as soon as the subscriber takes his telephone from its switch the line will test busy whether or not it is switched at the central office. Again, in systems of testing which depend only on a subscribers telephone being on or off its switch confusion frequently occurs from the fact that a subscriber places his telephone on its switch without sending in a clearing-out signal and his line tests free and is connected to when it is already switched at the central office with some other line. Lines in this condition are technically called tied up. In this system, again, this trouble is obviated, because the line will test busy until it is disconnected at the central office whether or not the subscribers telephone is on its switch. The system therefore combines the advantages and obviates the dis advantages of the two general systems of testing outlined above.

I claim as my invention and desire. to secure by Letters Patent- 1. A test-circuit for a subscribers line,fro1n the oifice ground through a test receiving instrument and battery to a test contact-plug, and thence to a line-contact when the test is applied; thence in one direction to the office ground through a comparatively high resistance, and in the other direction to the subseribers ground through a pair of switch contact-points in the central office and the subscribers-station apparatus, in combination with a switch-plug which separates said pair of contact-points while it switches the line and a condenser and a switch apparatus and circuits at the subscribers station toswitch said condenser into the circuit of the line when the telephone is switched for use, and thereby practically open the line-circuit to battery-currents, said test receiving instrument being adjusted to respond to current of certain strength, but not to respond to current of considerably less strength, and said instrument and battery being adjusted to each other and to the several resistances and the circuits to the degree that the instrument sounds when, on the test being made, neither the telephone nor the line is switched for use and not otherwise, substantially as set forth.

2. A test-circuit fora subscribers line,from the office ground through a test receiving instrument and battery to a test contact-plug, and thence to a line-contact when the test is applied, thence in one direction to the office ground through a comparatively high resistance and in the other direction to the subscribers ground through a series of pairs of switch contact-points, one on each of several boards, in combination with switch plugs adapted to be inserted into the switches for switching and when a plug is inserted into a switch to separate its pair of contact-points while the line is thus switched for use, and a condenser and switch apparatus and circuits at the subscribers station to switch said condenser into the line-circuit while his telephone is switched for use, and thereby practically open the line-circuit to battery-cur:

to a line contact-point when the test is applied, thence in one direction to the office ground through a comparatively high resistance, and in the other direction to the subscribers ground through a pair of switch contact-points in the central office and the subscribers-station apparatus, and abattery in the circuit, in combination with a switchspond to current of certain strength, but

not to'respond to current of considerably less strength, and said instrument and battery being adjusted to each other and to the several resistances and the circuits to the degree that the instrument sounds when, on the test being made, neither the telephone nor the line is switched for use, but not otherwise, substantially as set forth. v

4:. In a telephone-exchange system, a subscribers line grounded at its outer end and having a condenser in its circuit in the station apparatus,while his telephone is switched for use, and a comparatively low resistance while it is not thus switched, a switch at the centraloffice having a pair of contact-points normally in contact but separated while the line is thereby switched for use, and a test contact-piece insulated from the rest, except by the circuit connections, said line passing through said pair of contactpoints, and

thence to said test contact-piece, in combination with a resistance-coil grounded on one side and connected on the other side to the line-circuit between the contact-points, and the test contact-piece, and a test receiving instrument with battery grounded on one side and connected on its other side to a test plug or device adapted, at the will of the operator, to be brought into connection with said test contact-piece, said instrument being adjusted to respond to current of certain strength, but not to respond to current of considerably less strength, and said instrument being adjusted to the battery and the several resistances and the circuits to the degree that it sounds when,

on the test being made, neither the subscribers telephone nor the line is switched for use and not otherwise, substantially as set forth.

5. In a telephone-exchange system, a subscribers line grounded at its outer end and having a condenser in its circuit in the station apparatus,while his telephone is switched for use, and a comparatively low resistance while the telephone is not thus switched, a

. series of switches at the central ofiice for said line, one switch on each of several boards, each having a pair of contact-points normally in contact, but separated while the line is thereby switched, and a test contact-piece insulated from the rest (except by the circuit connections), said line passing successively through its said pair of contact-points, and thence to said test contact-piece, in combination with a resistance-coil grounded on one side and connected on its other side to the line after it has passed through said pairs the circuits to the degree that it sounds when,

on the test being made, neither the subscribers telephone nor the line is switched for use, but not otherwise, substantially as set forth.

6. In a telephone-exchange system, a subscribers line grounded at its outer end and having a condenser in its circuit at his station apparatus, while his telephone is switched for use, and comparatively low resistance while it is not thus switched, in combination with a series of test contact-pieces, one piece on each of several boards, and normally connected to the line, switch contact-points which disconnect the line from its said contact-pieces while it is switched for use, a resistance-coil connected on one side to said contact-pieces and grounded on the other side, in combination with test receiving instruments, one at each board, each grounded on one side and connected on its other side to a test-plug adapted to be brought for testing into connection with the test contact -piece at its board, said instrument being adjusted to respond to current of certain strength, but not to respond to current of considerably less strength, and said instrument being connected in circuit with a battery and adjusted to it and the several resistances and the circuits to the degree that it will sound when, on the test being made, neither said telephone nor the line is switched for use and not otherwise, substantially as set forth.

7. In a telephone-exchange system, a subscribers line grounded at its outer end and havinga condenser in its circuit at his station, while his telephone is switched for use and comparatively low resistance while the telephone is not thus switched, multiple switchboards, switches for the line, each having a pair of contact-points normally closed but open while the line is switched at its board, test contact-pieces, one on each board, and a resistance-coil grounded on one side, said line passing successively through said pairs of contact-points and thence connected to said test contact-pieces and to the other side of said resistance-coil, in combination with test receiving instruments, one at each board, grounded on one side and connected on its other side to a test plug or device adapted to he brought for testing into connection with the test contact-piece at its board, said instrument being adjusted to respond to current of certain strength, but not to respond to current of considerably less strength, and said instrument having a battery in circuit with it and adjusted to the battery and the several resistances and the circuits to the degree that it will sound when, on a test being [0 made, neither said telephone nor the line is switched for use and not otherwise, substantially as set forth.

MILO G. KELLOGG.

\Vitnesses:

FRANCES D. KELLOGG, MARGARETHA RIEHL. 

